1. Field of the Invention
The present invention relates to a stage apparatus, and preferably to a stage apparatus that positions a substrate for an exposure apparatus.
2. Description of the Related Art
For the manufacture of highly integrated semiconductor devices, an exposure apparatus is requested that can precisely position substrates to which patterns are to be transferred. As a propelling source for a stage apparatus to be used for such positioning, attention has been called to a so-called plane motor. A plane motor can be a variable-reluctance propelled type, for example, or an electromagnetic propelled type for which the Lorentz force is used.
An example plane motor of a variable-reluctance propelled type (hereinafter referred to as a plane pulse motor) is described in Japanese Patent Laid-Open Publication No. Hei 11-190786. In Japanese Patent Laid-Open Publication No. Hei 11-190786, comb-toothed magnetic members are arranged to constitute a stator, and opposite the stator, a plurality of coils having comb-toothed portions, a permanent magnet and a yoke are arranged to constitute a moving element. With this arrangement, a current flows across the coils to change magnetic resistances and to exert a thrust for propelling the moving element. Further, a pulse current supplied to each coil is controlled to activate a stepping operation.
For the above described plane motor, a large current must be supplied to the coils to obtain a strong thrust, and heat generated by the coils becomes a problem. According to one method employed to overcome this problem, a coolant is used to cool the coils directly; however, space allocated for a coolant flow path must be increased if the coil cooling capability is to be improved, and accordingly, the overall size of the apparatus is increased. This increase in size also results in an increase in the size of a moving stage when the coils are provided in the moving section. Further, when the flow rate of the coolant is increased, vibration caused by the coolant flow can cause a disturbance. As a result, these problems hinder the achievement of an increase in accuracy.
Further, when the coils are exposed as in Japanese Patent Laid-Open Publication No. Hei 11-190786, heat generated by the coils adversely affects the optical measurement path of an interferometer provided to obtain measurements used to establish the location of the moving element, thereby reducing the positioning accuracy. These problems will be even more noticeable when, to increase the propelling force, an arrangement including many coils is employed.